Water Distribution Operator Class II key terms

An underground layer of sand, gravel, or rock that holds and transmits water in quantities large enough to supply wells or springs. Confined aquifers sit under a low-permeability layer; unconfined aquifers have a water table open to recharge.

The maximum rate at which water can be withdrawn from a source over time without depleting storage, degrading water quality, or harming other users and the environment. It is the planning ceiling for a supply source.

The highest rate of water use a system must supply during a defined period, such as a day or an hour. Storage, pump capacity, and main sizing are planned around it.

The rate of water a system must deliver at a specified residual pressure for firefighting, in addition to normal domestic demand. It is a common driver of main size and storage volume.

The level of water in a well when the pump is off and the water has recovered to its natural level. Comparing it with the pumping level shows how much the well draws down under use.

The drop in water level in a well or aquifer caused by pumping. Excessive drawdown can reduce yield, expose the pump intake, or pull in poor-quality water.

The volume of water a well can produce per unit of time, usually expressed in gallons per minute, measured under a specified pumping condition. It is confirmed by a pump test rather than by the driller's estimate alone.

A valve with a sliding gate that opens fully to give a straight, low-loss flow path. It is used for isolation rather than throttling, because a partly open gate erodes and chatters.

A quarter-turn valve with a rotating disc mounted on a shaft inside the pipe. It is compact and low-cost for isolation service but leaves the disc in the flow path, so it adds some head loss.

A device installed at high points of a main that automatically vents accumulated air while the line is under pressure. Trapped air restricts flow, causes noisy operation, and can distort flow meter readings.

A valve that admits air into a pipe when internal pressure drops, preventing a vacuum that could collapse thin-wall pipe or siphon backflow. It closes when the line refills and repressurizes.

A mass of concrete poured against a fitting such as a tee, bend, or cap to resist the unbalanced pressure force that tries to push the fitting off the pipe. It is a standard restraint method on buried mains.

A flanged pipe joint in which a rubber gasket is compressed by a follower gland tightened with bolts. It allows some deflection and is commonly used where a restrained, dismountable joint is needed.

A bell-and-spigot joint in which a lubricated rubber gasket seated in the bell seals against the spigot as it is pushed home. It is fast to assemble but needs separate restraint against pullout forces.

The formation and collapse of vapor bubbles in a pump or valve where local pressure falls below the liquid's vapor pressure. It causes noise, vibration, and progressive damage to impellers and casings.

The margin of absolute pressure above a liquid's vapor pressure at the pump suction, required to keep the liquid from boiling in the pump. Insufficient NPSH available causes cavitation.

A graph showing how a pump's head, efficiency, and power draw change across its range of flow rates. The operating point is where the pump curve crosses the system curve.

A plot of the head required to move water through a given piping system at various flow rates, combining static lift and friction losses. It shifts when valves, tanks, or demand change.

Relationships describing how changing a centrifugal pump's speed or impeller diameter changes flow, head, and power. Flow varies with speed, head with speed squared, and power with speed cubed.

An electronic controller that changes a motor's speed by varying the frequency of the power supplied to it. It lets pumps match demand, saving energy and reducing pressure swings in the distribution system.

A pressure surge caused by a sudden change in flow velocity, such as rapid valve closure or pump trip. The shock wave can rupture pipe and damage fittings, so slow-closing valves and surge protection are used.

A valve that automatically lowers a higher upstream pressure to a steady, lower downstream pressure. It protects downstream piping and appliances and is common in pressure zones fed from high ground or pumps.

A portion of a distribution system kept within a defined pressure range by a boundary device such as a pressure reducing valve or a booster pump. Zones prevent excessive pressure at low elevations and low pressure at high elevations.

The pressure remaining at a point in the distribution system while water is flowing. It is measured during fire flow tests and indicates whether the system can meet demand without dropping below minimum standards.

The energy lost to resistance as water flows through pipe, fittings, and valves, seen as a drop in pressure along the line. It rises with flow rate, roughness, and smaller pipe diameter.

The concentration of chlorine remaining in water after treatment and travel through the system. A measurable residual shows the water is still protected against microbial contamination.

A measure of disinfection strength calculated by multiplying disinfectant residual concentration by contact time. Regulations set minimum CT values for killing or inactivating pathogens such as Giardia and viruses.

Compounds such as trihalomethanes and haloacetic acids that form when disinfectants react with naturally occurring organic matter in water. They are regulated because long-term exposure poses health risks.

A measure of the organic material in source water that can react with disinfectants to form byproducts. Utilities monitor and remove it through coagulation and filtration to control byproduct formation.

The cloudiness of water caused by suspended particles such as clay, silt, and organic matter. High turbidity can shield pathogens from disinfection and is a regulated treatment indicator.

Any actual or potential link between the potable water system and a source of nonpotable water or other substance. If a pressure reversal occurs, contaminants can be drawn or pushed into drinking water.

The unwanted reversal of water flow in a piping system, opposite to the intended direction. It is caused by backsiphonage, where supply pressure drops, or backpressure, where downstream pressure exceeds supply pressure.

An unobstructed vertical space between a water supply outlet and the flood level rim of the receiving vessel. It is the highest level of protection against backflow because it relies on physical separation, not a mechanical device.

An assembly such as a reduced-pressure-zone device or double check valve that stops reverse flow. Reduced-pressure assemblies protect against both backsiphonage and backpressure and require annual testing.

A water sample collected in a sterile container, dechlorinated if needed, and analyzed for coliform bacteria. Proper collection technique and chain of custody are essential because contamination during sampling invalidates results.

A space large enough to enter, with limited entry or exit, not designed for continuous occupancy. Permit-required confined spaces such as vaults and wet wells demand atmospheric testing, attendants, and rescue provisions before entry.

A procedure for isolating and de-energizing equipment, then locking and tagging it, so it cannot be started while someone works on it. Only the person who applied the lock removes it.

A protective system of supports, shields, or sloping that prevents trench walls from collapsing onto workers. It is required for excavations at depths where cave-in hazards exist and is a leading cause of utility fatalities.

A short, job-specific safety briefing held at the work site before a task begins. It covers hazards, procedures, and emergency plans and gives crew members a chance to raise concerns.

An annual report a community water system must deliver to its customers describing source water, detected contaminants, and compliance with drinking water standards. It is a public right-to-know requirement under federal rules.

The highest concentration of a regulated contaminant allowed in drinking water, set as close to the health goal as is feasible with available treatment. Compliance is judged by prescribed monitoring and averaging rules.

The required process of informing customers when a water system violates a drinking water standard or faces a risk to public health. The form and deadline depend on the severity of the violation.